Nii-chan (harada)
Complete | Harada | 2013 released
Even though the events are disgusting the plot is redacted realistically, not that Yui and Kei end up as a couple but because of the explanation of tbe fucking cycle of abuse. If not treated the victim often becomes the abuser, and this repites again and again till one of the victims is either treated and cared about (and end the cycle)
Raise wa Tanin ga Ii